Identification of biogenetic calcite and aragonite using SEM
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Abstract
Identification of calcite and aragonite is very important for studying different fossil or recent biomineralized skeletons. Problem occurs when scanning electron microscopy is used for studying calcite and aragonite present in the same part of skeleton. The same chemical composition of these two minerals produces the same contrast on SEM images. There are three possible ways how to distinguish calcite and aragonite in such mixture.
(1) It is possible to recognize the crystal habits of these two minerals, if the crystal faces are developed.
(2) Geochemical difference could be also important tool for distinguishing aragonite (containing large cations like Sr, Ba, or Pb) from calcite (containing small cations like Mg, Mn, Fe, Zn, or Ni). However, it is also possible that large cations remain in calcite crystal structure after phase transformation from aragonite to calcite.
(3) Last possibility in distinguishing calcite from aragonite is to use staining methods. There were different staining methods used for SEM analyses with different success. SUZUKI et al. (1993) successfully used Meigen’s staining method, but results provided by Feigl’s staining method were unsatisfactory. Failure of using Feigl’s staining method was caused by erroneous applying of used solutions.
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